1. Field of the Invention
The present invention is in the field of medicinal chemistry. In particular, the invention is related to vaccines comprising a saponin, the process for production thereof, and the use thereof to immunize animals.
2. Brief Description of the Background Art
Quillaja saponins are a mixture of triterpene glycosides extracted from the bark of the tree Quillaja saponaria. Crude saponins have been extensively employed as adjuvants in vaccines against foot and mouth disease, and in amplifying the protective immunity conferred by experimental vaccines against protozoal parasites such as Trypanosoma cruzi plasmodium and also the humoral response to sheep red blood cells (SRBC). (Bomford, Int. Arch. Allerg. Appl. Immum. 67:127 (1982)).
Saponins are natural products which have been characterized by a number of common properties. The ability to produce foam in aqueous solution gave the name to the group. Further characteristics are the hemolytic activity, the toxicity for fish, the complexing with cholesterol, and in some cases antibiotic activity. Kofler, Die Saponine (Springer Berlag), Berlin, 1927; Tschesche et al., Chemine und Biologic der Saponine, Fortscher. Chem. Org. Naturst. XXX:461 (1972).
The common properties of saponins are not reflected in a common chemical composition. Although all saponins are glycosides, the aglycone may belong to the steroids, the triterpenoids, or the steroidalkaloids. The number of sugar and sugar chains attached to the glycosidic bonds may vary greatly. Saponins have been produced commercially and have many uses. The commercially available Quillaja saponins are crude mixtures which, because of their variability, are not desirable for use in veterinary practice or in pharmaceutical compositions for man. Because of the variability and heterogeneity, each batch must be tested in animal experiments to determine adjuvant activity and toxicity. The impurities in the commercially available products may produce adverse reactions. In addition, the content of the active substance in a given batch of saponin may vary, thereby decreasing the reproducibility from batch to batch.
An early attempt to purify Quillaja saponin adjuvants was made by Dalsgaard, Archiv fuer die gesamte Virusforschung 44:243 (1974). Dalsgaard partially purified an aqueous extract of the saponin adjuvant material from Quillaja saponaria Molina. Dalsgaard's preparation, commercially available from Superfos under the name "Quil-A," has been isolated from the bark of the South American tree, Quillaja saponaria Molina, and is characterized chemically as a carbohydrate moiety in glycosidic linkage to the triterpenoid quillaic acid. However, while the saponin Quil A of Dalsgaard presents a definite improvement over the previously available commercial saponins, it also shows considerable heterogeneity.
Higuchi et al., Phytochemistry 26:229 (January, 1987) treated a crude Quillaja saponin mixture with alkaline hydrolysis in 6% NH.sub.4 HCO.sub.3 in 50% methanol and generated two major desacylsaponins, termed DS-1 and DS-2. DS-1 was shown to contain glucuronic acid, galactose, xylose, fucose, rhamnose, apiose, and Quillajic acid, whereas DS-2 contained these same components plus an additional glucose. Byproducts of this deacylation produced multiple components including 3,5-dihydroxy-6-methyloctanoic acid, 3,5-dihydroxy-6-methyloctanic acid-5-0-.alpha.-L-arabinofuranoside and -5-O-.alpha.-L-rhamnopyranosyl-(1.fwdarw.2)-.alpha.-L-arabinofuranoside (H iguchi et al., Phytochemistry 26:2357 (August, 1987).